The implementation of a surgical implantation of the prior art vertebral locking and retrieving system requires that the spinal pins or the Lugue hooks which are inserted into vertebrae must be aligned. If a surgeon performing the surgical operation fails to attain such an alignment of the spinal pins or the Lugue hooks, he or she is forced to remedy the situation by bending the locking rod of the implanted system. Such a practice is not desirable because it often fails to bring about a satisfactory result of stabilizing the vertebrae under treatment.
With a view to overcoming the serious drawback of the prior art system described above, a variety of improved systems are disclosed in the U.S. Pat. Nos. 5,030,220; 4,827,918; 5,053,034; and 5,047,029. In addition to the above-identified patents, an improved system known as Diapason is disclosed by a French Company called Dimso. All these improved systems are by no means free from shortcomings. The improved system disclosed in the U.S. Pat. No. 5,030,220 is defective in design in that the clamp located at the curved portion of the locking rod can not be fastened effectively and that the clamp is capable of making only a unidirectional adjustment of the fastening angle of the spinal pins. The Diapason system has an advantage that it can be rotated in all directions; nevertheless it lacks an efficient locking effect in view of the fact that it is provided with the curved locking rod and that its spinal pins are ineffective when used at a location slightly far away from the locking rod. The systems of the U.S. Pat. Nos. 4,827,918; 5,047,029; and 5,053,034 are also limited in that they can be caused to make an angular adjustment of the spinal pins in only one direction, or in two directions at best, and that they are vulnerable to a mechanical failure due to their complicated structural make-up.